Caracterização da expressão do estro e seu impacto sobre a fertilidade de distintas categorias de fêmeas zebuínas submetidas a IATF

Abstract

The objective of this study was to evaluate the oestrus expression profile, as well as the impact of oestrus on the fertility of different categories of zebu females submitted to a FTAI protocol. For this purpose, 1053 females were used (658 multiparous, 138 primiparous and 257 heifers), synchronised with the following hormonal protocol: on day 0 (D0), the animals received a 0.5 g intravaginal progesterone releasing device combined with 2 mg of oestradiol benzoate intramuscularly (IM). On D8, the P4 intravaginal device was removed and 300 IU of equine chorionic gonadotrophin was administered IM, 520 μg of cloprostenol sodium IM and 1 mg of oestradiol cypionate IM. At this point, the animals were tagged with a marker stick between the sacral tuberosity and the insertion of the tail to determine oestrus expression. On D10, the animals were divided into two experimental groups: Group without estrus expression ("WITHOUT ESTRUS") and Group with estrus expression ("WITH ESTRUS") by removing the dye. Immediately after characterisation of estrus expression, FTAIs were carried out. On D20, the females were exposed to bulls at a 1:30 ratio. In order to determine the pregnancy rate after FTAI (PRFTAI), the pregnancy rate after bull exposure (PRbe) and the breeding season pregnancy rate (PREnd) two pregnancy diagnoses were performed. FTAI pregnancy diagnosis was carried out by ultrasonography on day 40 (D40). The gestational diagnosis after bull exposure and the final diagnosis of the breeding season were carried out at the end of the breeding season (D130). Statistical analyses were carried out using R Software, using the STATS package (2023), and a significance level of 5% was considered. The overall estrus detection rate (ODR) was 67.04% and there was no difference between the reproductive categories (heifers= 72.76%; primiparous= 61.59%; multiparous= 65.95%). The overall PRFTAI was 62.11%, also showing no difference between the categories (heifers = 65.36%; primiparous = 62.31%; multiparous = 60.79%). The overall PRbe was 68.17%, with no difference between the reproductive categories (heifers= 66.29%; primiparous= 61.54%; multiparous= 70.15%). The overall FinalPR was 84.99%, with no statistical difference between the reproductive categories (heifers= 88.33%; primiparous= 84.05%; multiparous= 83.89%). With regard to the influence of estrus on the fertility of the heifer category, estrus had a positive impact on PRFTAI (with oestrus= 71.65% vs. without oestrus= 48.57%; P<0.01). However, no statistical difference was observed with regard to PRbe (with estrus= 64.15% vs. without estrus= 69.44%; P=0.61) and the PREnd (with estrus = 89.84% vs. without oestrus =84.28%; P=0.81). For the primiparous females, there was no difference between the experimental groups WITH ESTRUS and WITHOUT ESTRUS for PRFTAI (62.35% vs. 62.26%; P=1.0), PRbe (59.37% vs. 65.00%; P=0,79) and PREnd (83.53% vs. 84.90%; P=0.90). Regarding the multiparous reproductive category, differences were observed (P<0.01) between the experimental groups WITH ESTRUS and WITHOUT ESTRUS regarding PRFTAI (68.20% vs. 46.43%), PRbe (78.98% vs. 60.00%) and the PREnd (88.94% vs. 74.11%). Therefore, estrus detection can be used as a tool to direct matings in synchronisation protocols in heifers and multiparous females, as well as the possibility of being used as an alternative to predict the results of a breeding season in the multiparous category.